Nature's notebook: Return of the Bald Eagle

The relatively common sightings of bald eagles wintering along waterways in the Capital District have an uncommon story in how our nation's symbol made a comeback from near extinction in the state. A team of biologists led by Peter Nye, now retired from 36 years of service in New York State's Endangered Species Unit, and others devised first a fostering program with chicks and then a very successful hacking program with juveniles to reintroduce bald eagles into suitable breeding territories.

I was able to hear Peter Nye speak recently about the restoration of the bald eagle to New York at a program by Audubon New York. Why were bald eagles by 1976 reduced to one breeding pair in New York? What was wrong that this pair could not raise young on their own? What were some of the factors of the bird's biology that enabled the Department of Environmental Conservation's team to jump-start the return using juveniles from out of state?

In 1782 when we adopted the bald eagle as our national symbol there were estimated to be 100,000 nesting pairs in America.

Because of habitat loss, illegal shooting, often because birds of prey were viewed as competitors for game, and contamination of their food sources, by 1963 there were only 487 nesting pairs, and the bird was in danger of extinction.

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DDT was the primary contaminant that built up in the food chain for these top predators. Bald eagles take fish as their staple food and live near rivers, lakes, and marshes to be close to their food supply. Peter Nye pointed out DDT was not the main cause of the bald eagle's decline, but the "straw" that proved too much for this species.

DDT caused the shells of the eagle's eggs to be thin and crack when the mother incubated them.

Observations of New York's last remaining eagle pair, nesting near Rochester, showed the female to by laying and attempting to incubate, but the eggs breaking. A fostering program was started by removing any egg, adding a plastic dummy egg for the birds to incubate, and replacing the plastic egg with a captive-bred chick after several weeks of incubation. The pair successfully raised a total of 8 chicks from 1975 to 1987 this way, however, the process was deemed too slow for overall bald eagle recovery in the state.

An inventory of past known bald eagle nest sites in the state was made with the purpose of serving as release or hacking sites for juvenile bald eagles brought in from other states as Alaska and Minnesota. Cornell's Dr. Tom Cade had been having success in bringing back peregrine falcons by hacking.

Peter Nye's team worked in conjunction with him to develop a similar program for bald eagles. Hacking involves building a protected nesting tower and raising juvenile birds until they can leave the tower nest by hand feeding behind a blind. In 1976 two juvenile bald eagles, Henry and Agnes, were brought in from Minnesota to a hacking tower at Montezuma National Wildlife Refuge.

For several years the birds returned to their release site, and in 1980 nested near Watertown and successfully raised a chick of their own.

Bald eagles exhibit nest site fidelity or a preference to return to the same general area they were raised. No one in the world had released or hacked bald eagles.

Peter Nye's team was the first to try it, and they found it worked better than expected. Between 1976 and 1988 198 eagles were released in New York this way, most collected as nestlings from Alaska.

This involved the New York team, with Alaska's and the Federal Governments' permission, climbing nest trees to collect the young birds, transporting them to New York, and feeding them lots of fish along the way. Eleven other states including Massachusetts, New Jersey, and Pennsylvania contacted the group on how to set up similar hacking programs of their own. Between the five states of Vermont, Massachusetts, New York, Pennsylvania, and New Jersey 409 eagles were hacked. The original hacking towers were modified into hacking condominiums for multiple releases. By 1989 the team's goal of 10 breeding pairs in New York was reached, and the program ended.

The success of the program can be seen in the more than 170 breeding pairs that nest in New York and the striking sights of bald eagles once again flying in our wild portions of Nature's Notebook.

Sandy de Waal Malefyt is a local nature enthusiast and science teacher.